Field of the Invention
Embodiments of the invention relate to an organic light emitting display encapsulation technology.
Discussion of the Related Art
Each pixel in an organic light emitting display includes an organic light emitting diode (OLED) having a self-emitting structure. As shown in FIG. 1, the OLED includes a stack of organic compound layers including a hole injection layer HIL, a hole transport layer HTL, an emission layer EML, an electron transport layer ETL, an electron injection layer EIL, etc., between an anode and a cathode. The organic light emitting display displays an image using a phenomenon, in which the OLED emits light when electrons and holes are combined in an organic layer through a current flowing in a fluorescence or phosphorescence organic thin film.
In addition, the organic light emitting display may be variously classified depending on kinds of emission materials, an emission method, an emission structure, a driving method, etc. The organic light emitting display may be classified into a fluorescent emission type and a phosphorescent emission type depending on the emission method. Further, the organic light emitting display may be classified into a top emission type and a bottom emission type depending on the emission structure. Further, the organic light emitting display may be classified into a passive matrix OLED type and an active matrix OLED type depending on the driving method.
However, characteristics of the organic compounds are sharply degraded when organic compounds of the OLED are exposed to moisture. Thus, the moisture penetrating into the pixels decreases the reliability and lifespan of the organic light emitting display. An encapsulation method is used to limit the degradation of the OLEDs resulting from the penetration of moisture and oxygen. One example of the encapsulation technology is disclosed in Korean Patent Laid-open Publication Nos. 10-2013-0055544 (May 28, 2013) and 10-2013-0058711 (Jun. 4, 2013) corresponding to the present applicant, and which are hereby incorporated by reference in their entirety.
In more detail, an encapsulation technology illustrated in FIG. 2 attaches a back plane BPL and an encapsulation plate ENC using an adhesive film ADH. The back plane BPL includes a pixel array OLED & TFT formed on a substrate. The pixel array OLED & TFT includes data lines, scan lines crossing the data lines, and pixels each including an OLED and a thin film transistor (TFT). The pixels are also arranged in a matrix form.
Further, the pixel array OLED & TFT are covered with a passivation layer PAS and are formed in an active area AA, on which an image is displayed. In FIG. 2, “PAD” denotes a data pad or a scan pad connected to an output terminal of a drive integrated circuit (IC) formed at an end of the data line or the scan line; “BZ” denotes a bezel on which the image is not displayed at an edge of a display panel; and “CAT” denotes a cathode of the OLED. In the encapsulation technology illustrated in FIG. 2, there is no barrier capable of blocking moisture (H2O) penetrating into the pixel array OLED & TFT. Thus, the reliability and the lifespan of the organic light emitting display adopting the encapsulation technology illustrated in FIG. 2 is reduced.
Another encapsulation technology is illustrated in FIG. 3 and includes a back plane BPL and an encapsulation plate ENC attached using an adhesive film ADH. Moisture absorption fillers GT are also added to the inside of the adhesive film ADH to help absorb and prevent the moisture from penetrating or exposing the pixel array OLED & TFT.
However, even though the moisture absorption fillers GT may increase the reliability and the lifespan of the organic light emitting display, the fillers GT are also distributed in the active area AA in FIG. 3. Thus, light emitted from the active area AA is scattered by the moisture absorption fillers GT, and the display image is blurred due to a haze effect. Therefore, it is difficult to apply the encapsulation technology illustrated in FIG. 3 to the top emission type organic light emitting display, in which light of the display image is emitted through the encapsulation plate ENC.